sctp: remove unreachable code from sctp_sf_violation_chunk()

sctp_sf_violation_chunk() is not called with asoc argument equal to NULL,
but if that happens it would lead to NULL pointer dereference
in sctp_vtag_verify().

The patch removes code that handles NULL asoc in sctp_sf_violation_chunk().

Found by Linux Verification Center (linuxtesting.org) with SVACE.
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Proposed-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/sm_statefuns.c

@@ -4898,9 +4898,6 @@ static enum sctp_disposition sctp_sf_violation_chunk(
 {
 	static const char err_str[] = "The following chunk violates protocol:";
 
-	if (!asoc)
-		return sctp_sf_violation(net, ep, asoc, type, arg, commands);
-
 	return sctp_sf_abort_violation(net, ep, asoc, arg, commands, err_str,
 				       sizeof(err_str));
 }